The present invention generally relates to image scanning apparatuses, and more specifically to an optical image scanning apparatus used for printers, facsimile machines, copy machines or digital scanners.
In many conventional copy machines, the size of an original sheet set in a copying position is detected before a copying operation is started. The detection of the size of the original sheet is generally performed by means of an optical system. One method of the detection of the size uses a scanner which is provided for reading an image on the original. This method does not require an additional optical system for detecting the size. However, this method takes time to scan the entire original sheet before an actual copying operation is started, and thus it takes a relatively long time to make a copy. Accordingly, users are dissatisfied with a copy machine in which this method is used.
Another method of detecting the size of an original sheet is to use an additional detecting device. Japanese Laid Open Patent Application No.4-178601 discloses an original sheet size detection system in which a grating array (hologram) is used in an optical detection system. FIG. 1 is an illustration of an example of an original sheet size detection system incorporated in a copy machine which system uses a hologram. FIG. 1 is a view of the inside of a scan table (contact glass) from directly above the contact glass.
In FIG. 1, three photosensor devices 2 are shown provided in predetermined positions, under a scan table which is made of transparent material such as glass. Each of the photosensor devices 2 comprises a hologram, a light source and a photosensor (not shown). A light beam emitted by each of the photosensor devices 2 is split into three beams a, b, c. Positions of the split light beams a, b, c at the scan table surface are shown in FIG. 1. The beams a, b, c are reflected by original sheet or other material, and the reflected beams return to the respective photosensors 2. The beams a, b, c are detected by the photosensors in the photosensor devices 2.
In the above-mentioned optical original sheet size detection system, since a light beam is split into three beams, three light sources are needed to emit light beams to direct the beams in nine directions, while nine light sources are needed in a conventional system. However, the above-mentioned system still requires at least three photosensors. Additionally, the sizes of the original sheet which can be detected are limited to predetermined sizes, for example a standard A-size sheet or B-size sheet, because the positions of beams projected on the scan table are fixed. Therefore, the above-mentioned optical original sheet size detection system cannot detect a sheet size other than one of the predetermined size.
An optical sensing device is disclosed in Japanese Laid-Open Patent Application No.53-117333. FIG. 2 is an illustrative perspective view of the optical information reading device disclosed in Japanese Laid-Open Patent application No.53-117333. This device is used as a bar code reader.
In FIG. 2, a laser beam emitted by a semiconductor laser 3 passes through a mirror having a hole, and is incident upon a hologram scanner (hologram disk) 6 rotated by a motor 5. The laser beam is deflected and concentrated, by hologram 6a formed on the rotating hologram scanner 6, onto the plane of a bar code 7 so that the laser beam scans the bar code as indicated by dotted line S.sub.o. The laser beam reflected by the bar code is incident upon the hologram 6a at a position different from the position on which the laser beam was initially incident, and passes through the hologram scanner 6. The laser beam is then reflected by the mirror 4 and incident upon a photodetector 8. Bar code information is obtained by analyzing the intensity variations of the laser beam detected by the photodetector 8.
The above-mentioned scanning method disclosed in Japanese Laid-Open Patent application No.53-117333 provides a simple optical detection system to recognize size and displacement of an original sheet by means of a simple construction. However, there has been suggested no image scanning apparatus using such a method in the art.